High tension wood structure free of radio interfering radiation and burning from leakage current



Aug. 27, 1968 J H. WILLO URE FREE OF R FROM Aug

X 3,399,269 7 HIGH TENSION WOOD STRUCT ADIO INTERFERING RADIATION ANDBURNING LEAKAGE CURRENT Filed 51, 1967 I INVENTOR. x LBAQ J! BY "Q TUnited States Patent 3,399,269 HIGH TENSION WOOD STRUCTURE FREE OF RADIOINTERFERING RADIATION AND BURNING FROM LEAKAGE CURRENT I Hebden Willox,917 Newcastle Ave.,

Westchester, II]. 60153 Filed Aug. 31, 1967, Ser. No. 664,682 6 Claims.(Cl. 174-45) ABSTRACT OF THE DISCLOSURE The adverse effects of (a) theburning of coniferous wood members of a high tension structure and (b)the generation of radio interfering sparking between closely spacedloose hardware is precluded by the interposition of a compressed helicalspring coil between the nut and head of the assembly bolts passingthrough and joining the wood members, the spring coil having more thanone full turn of quadrilateral cross section and flattened arcuate endsurfaces coated with a malleable metal softer than the metal forming thecoil.

This invention relates generally to wood structures for supportingoverhead high voltage energized electric conductors, and specifically tothe combination therewith of means effective to provide a structurewhich is free of both leakage current burning damage and generation ofradio interference in the standard broadcast band and the VHF or UHFfrequency ranges.

The advantages of wood members over metal members for high voltage kv.and above) electric lines has long been recognized; lower cost andinherent insulating qualities being among the more important. Coniferoussoft woods, such as pine and fir, are relatively inexpensive and arereadily treated with preservative liquids carrying creosote orpenta-chlorophenol. For these reasons, conife'rous wood members arefound almost exclusively in wood pole line construction.

As the dielectric strength of the'insulation, including a pine pole anda fir crossarm, varies from time to time with the moisture content ofthe wood and with surface contamination, such as salt spray alongcoastal areas, the magnitude of the leakage current from an associatedenergized conductor similarly increases and decreases. Wood tracking andburning at points of concentration of leakage current, and radioinfluence and interfering radiation from induced voltage sparkingbetween loose, closely spaced hardware elements are important adverseeffects which can be --satisfacto'rily precluded if the contact betweenthe wood members and between the components of the associated metalfasteners is maintained under continuous pressure applied over asufficiently large area of engagement of the abutting surfaces.

Contra to the achievement of this desired condition are the naturalchanges in the dimensions of the wood members under weatheringconditions, as well as their inherent low side-grain surface hardness,the latter permitting a limited but significant indentation of the woodas the abutting fastener element is continuously pressed against thewood surface.

The correlated problems of leakage current wood burning and radiointerference due to loose and corroded connecting hardware has long beenrecognized by the electric utility industry. Numerous constructions havebeen utilized in attempts to solve the problems, including the use ofnumerous shapes of single turn lock washers, lacking, as they do, thesubstantial axial resilient movement necessary to compensatefordimensional change of the wood-members. Currently several shapes ofhairpin spring washers are in use. In addition to being bulky andcostly,

3,399,269 Patented Aug. 27, 1968 hairpin washers, when compressed,effect substantially point contacts with the facing members, instead ofthe desired distributed pressure, with resultant hot spots at the woodsurface from leakage current concentration. Simple helical coil springsof round or rectangular section with square cut ends lack the criticallyrequired bearing area, as well as its critical location, and absent theimportant end tapering, tend to fracture distally from the ends undercontinuous compressive stress. In addition, square cut ends act ascutting tools upon the mating surfaces, and thus destroy the value ofany rust-preventing coating which they may engage.

It is an object of the present invention to provide a leakage-currentdamage and radio interference free high tension structure embodyingconiferous wood structural members, achieved by the associationtherewith of a spe cifically adapted fastener construction.

Another object is to provide, in a bolted crossarm assembly, acompressed spring coil interposed between an end of the bolt and thesurface of the crossarm through which the bolt passes, the coil beingcharacterized by (a) an open helical winding of about 30 degrees lessthan two full turns; (b) a winding from a wire having a trapezoidal orkeystone cross section; (c) the ends being tapered to provide flatmating surfaces and to facilitate bending thereof to conform to themated surfaces; and (d) the mating surfaces being coated with a soft andmalleable metal; e.g., tin, lead or cadmium.

A further object is to provide an assembly embodying a helical springlock washer of the foregoing characteristics which will function tomaintain a continuous pressure upon both the hardware elements of thefastener and the associated wood members under all service conditions,including particularly any and all changes in texture and form to whichconiferous woods are susceptible under outdoor weathering.

Another object is the provision of an assembly embodying a helicalspring lock washer having no square cut ends or sharp points, thisfeature enabling reuse of galvanized hardware since the corrosionprotection is not scraped away upon either installation or removal.

An embodiment of the invention is illustrated in the accompanyingdrawing, in which:

FIG. 1 is a perspective view of an upper portion of an electric overheadline structure, showing an exemplary application of the invention;

FIG. 2 is an enlarged section, taken along the line 22 of FIG. 1, inwhich the fastener elements are drawn twice actual size;

FIG. 3, is a plan view of the helical spring lock washer;

FIG. 4 is a section taken along the line 4--4 of FIG. 3, and

FIG. 5 is a fragmentary section of an end surface of the helical springlock washer of the invention.

FIG. 1 shows the upper portion of an upstanding wood pole line structurein which the transversely extending wood crossarm 11 has mounted thereonthe insulator 12, to which is attached the energized electric conductor13. The metal through bolt 14 passes through both the pole 10 and thecrossarm 11, for the purpose of jointing these members in abuttingrelationship. One quite common arrangement of the members is a pine poleand a fir crossarm. The fastener elements associated with the bolt 14are shown more completely in FIG. 2, from which it may be seen that themetal washer 20 is interposed between the pole 10 and the bolt head 21,and the metal washer 17 along with the compressed helical spring lockwasher 16 are interposed between the crossarm 11 and the nut 15, thelatter threadedly engaging the outwardly extending end of the bolt 14.

As the fastener elements are combined in FIG. 2, the bolt 14 is intension as the result of tightening the nut 15 to compress the helicalspring washer 16, and the washers 17 and 20 are continuously urgedagainst the crossarm 11 and the pole 10 respectively, and, as hereillustrated, have indented the soft wood members, as indicated by thenumerals 18 and 19.

One function of the helical spring washer is to compensate for anychanges in form of the wood members, whether due to change in moisturecontent or to deformation of the soft wood under pressure. I have founda compressed-condition axial lengthening of the helical spring washer ofthe order of A to be a critical requirement in connection withconiferous wood members, as here illustrated, for continuouslymaintaining the necessary stress upon all the associated parts toobviate leakage-current wood burning and aperiodic radio interferingradiation. This resilient expansion requirement is substantially morethan that provided by any practicable single turn design, but slightlyless than that provided by the most economical open turn helix of twoturns. The smooth and wide area soft metal bearing surface, correctlydisposed at each end of the helical spring washer, is essential for thecontinuous proper functioning of the assembly.

As shown in FIG. 2, the particular structure of the helical springwasher, which is the critical element of the assembly, is an open turnhelix of more than one turn and less than two turns. The metal wire ofthe coil is trapezoidal or keystone in cross section, with an open turnspacing as indicated at 27. The cross section is shown in FIG. 4. Inthis embodiment one parallel side of the trapezoid, indicated at 23,forms the inner periphery of the coil, and the other parallel side 24forms the .outer periphery of the turns. A suitable material for thecoil is SAE 1060 wire, formed on a machine having rolls of 4 /2 degreestaper. After winding, the material is hardened and drawn to a Rockwell Cscale hardness not less than 40, -44 to C-46 being a desirable range.

Each end of the helix is severed along a plane coextensive with the axisof the helix and which diverges at an angle .of at least fifteen degreesfrom a plane coextensive with the axis of the helix which would passthrough both ends of a two full turn helix, and indicated in FIG. 3; inother words, the helix of the embodiment shown lacks thirty degrees ofhaving two full turns.

Each end portion of the coil is ground to provide the terminal flatsindicated at 25 and 26 of FIGS. 3 and 4. In so doing, at least one-halfof the keystone section at each end is removed, thus presentingidentical wide bearing end surfaces along the circumferentially spacedend portions extending through an angle of about 120 degrees from eachend of the coil. The shape of one of the end surfaces is indicated at 25of FIG. 3, from which it may be seen that the specified disposition ofthe keystone cross section results in a bearing surface along the innerperiphery of the arcuate end portion extending convolutely beyond thebearing surface along the outer periphery, thereby increasing the totalavailable bearing surface.

The flattened end surfaces 25 and 26 are plated with tin or other softmetal, as indicated by the fragmentary section of FIG. 5, for thepurpose of reducing the friction at each end of the washer when it iscompressed by turning a nut thereagainst. The relatively soft andmalleable metal acts as a spread under sliding frictional stress,lubricating the abutting surfaces. Further, the soft metal readilyspreads to fill pin holes or other holidays of an engaged protectivecoating, which, if remaining unsealed, expose rust-prone metal tocorrosive deterioration. The invention herein effectively precludes thedegradation of corrosion resistant protective coatings, such as zincgalvanizing, which are commonly destroyed by the use of locking deviceshaving sharp square cut ends, the latter functioning only by biting intoand shearing away the protective coating .of the contacted components.The corrosion products of pole line hardware are non-conductors, and

corroded loose hardware is the ideal combination for the generation ofadverse radio-influencing radiation from high voltage lines.

The thirty degree circumferential spacing between the ends of thehelical coil, in cooperation with the half-stock grind removal and thekeystone shape and disposition, effectively eliminate two seriousproblems presented by all helical washers having unchamfered ends. Oneofthese is the deflection of the washer from its desired coaxial positionwith respect to the associated bolt, which may so bend the latter as tocause ultimate failure. Another is the innate tendency to overstress themetal at the center of the coil when fully compressed. In applicantsstructure, the chamfered ends, together with theirmutually relatedcircumferential positions, permit the ends to resiliently deform underless stress than that required to deform the full-thickness turn portionof the coil. The necessary resilient axial movement is obtained throughthe resilient urging of the weakened ends toward the midpoint of thecoil, a gradually increasing pressure being equally applied on oppositesides of the associated bolt as the nut is turned, thus limiting themidpoint stress to a safe value even when the coil is fully compressedto turn-to-turn abutting engagement.

The permanently hardware-tight transmission line structure disclosedherein is equally effective for the prevention of (a) leakage-currentburning and (b) radio interfering radiation, despite the fact that theconditions favorable for the former differ widely from those favorablefor the latter. Leakage-current burning is caused by a concentration ofthe current due to poor or point contacts in the current path, such asmay result from loose hardware, and is most apt to occur in wet orcontaminated atmospheres. On the other hand, radio interference iscaused by induced sparking between closely spaced loose hardware, and ismost apt to occur under dry and uncontaminated atmospheric conditions.In either situation, the basic cause is unstressed or relaxed structuralcomponents of unsuitable shape, and this basic cause is effectivelyeradicated by applicants construction as recited herein..

While I have in the foregoing described and illustrated an embodiment ofthe invention, it will be apparent that changes and modifications mayreadily be made by those skilled in the art. It is therefore intendedthat the drawing and description shall be regarded as illustrativerather then limiting, reference being made to the appended claims toascertain the scope of the invention.

-What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In an electric transmission line structure including a coniferouswood member, an energized conductor insulatingly mounted thereon, andmetal fastener elements associated therewith including a metal bolthaving a head at one end and a threadedly engaged nut at the other end,said bolt extending through said wood member for effecting an attachmentthereto, said structure being susceptible both to wood burning fromleakage current and to generation of radio interfering sparking due todistortion or loosening of said metal fastener elements, the improvementcomprising the interposition of a compressed helical spring metal coilbetween said nut and the head of said bolt, said helical coil havingmore than one full turn of a wire of trapezoidal cross section, theparallel sides of the trapezoidal wire extending respectively along theinner and outer periphery of the helical turns and the end surfaces ofan arcuate end portion at each end of the coil lying in transverselyextending parallel planes, said end surfaces having disposed thereon alayer of a metal softer and more malleable than the metal forming thecoil.

' 2. The transmission line structure according to claim 1, in which thehelical spring coil extends convolutely through an angle of not morethan 340 degrees and not less than 320 degrees beyond one full turn.

3. The transmission line structure defined in claim 2, wherein the endsurfaces of the helical spring coil lie in axially spaced parallelplanes extending normal to the axis of the coil and around therespective arcuate end portions through an angle of at least 120 degreesfrom each end thereof.

4. The transmission line structure according to claim 3, in which therespective ends of the coil lie in planes intersecting at the coil axiswhich diverge from one another at an angle of not more than thirtydegrees.

5. The transmission line structure defined in claim 4, in which themetal forming the coil is a steel drawn to a Rockwell hardness of notless than C-40, and the metal layer disposed over the end surfaces istin.

6. In an electric transmission line structure which includes aconiferous wood member, an energized conductor insulatingly mountedthereon, and metal fastener elements associated therewith including ametal bolt having a head at one end and a threadedly engaged nut at theother end, said bolt extending through said wood member for effecting anattachment thereto, the improvement comprising means for precludinginduced radio interfering sparking between loosened metal fastenerelements, said means including the interposition of a compressed helicalspring metal coil between said nut and the head References Cited UNITEDSTATES PATENTS 152,864 7/ 1874 'Pickels 26 7-61 303,302 8/1884 Ludlum26761 501,052 7/1893 Brown 151-38 X 2,943,870 7/ 1960 Davis 267-1 XFOREIGN PATENTS 732,313 6/ 1955 Great Britain.

OTHER REFERENCES Carlson, Stainless Steels for Springs, ProductEngineering, May 1947, pp. 103-406.

25 LARAMIE 'E. ASKIN, Primary Examiner.

